The present invention relates to wiring devices for feeding power or signals, for example, to the optical assembly of image forming apparatus such as analog copying machines, digital copying machines and facsimile systems, or to the printing head of serial printers.
Image forming apparatus such as analog copying machines are heretofore available in which an optical assembly is moved to illuminate and scan a document placed on the document support plate for exposure.
FIG. 6 shows an optical system including such a movable optical assembly. The system comprises a light source 101 for illuminating documents, and mirrors 103, 104, 105, 106 and a lens 107 for directing the reflected light from the document to a photosensitive member 102. The light source 101 is supported on an unillustrated movable frame and reciprocatingly moved along a document support plate 108. A power supply cable 109 is connected to the light source 101.
However, the cable 109 is thick, heavy and low in flexibility, therefore heavily burdens the movable frame during the movement of the optical assembly and causes vibration of the optical assembly.
Accordingly, a flexible printed wiring board has recently been placed into use instead of the cable 109. The flexible printed wiring board is prepared by printing the desired circuit on a light flexible polyimide film.
The flexible printed wiring board is indicated at 110 and shown in FIG. 7 (A). The wiring board has one end connected to the movable frame carrying the light source 101, is bent approximately to a U-shape at an intermediate portion, and is fixed at the other end thereof to an immovable portion of the machine body.
However, when the light source 101 is in the home position (at the left of FIGS. 7 (A), (B) and (C)), the bent portion of the wiring board is away from the light source 101, so that the upper side portion of the board 110 is likely to sag under its own weight as seen in FIG. 7 (B). If the light source 101 moves as indicated by an arrow with the wiring board 110 in such a sagging state, the sagging portion is further bent downward as shown in FIG. 7 (C) to give rise to the problem of imposing an unnecessary burden on the movable frame carrying the light source 101, causing vibration to produce blurred images or possibly causing a break in the printed wiring on the board 110.
The wiring board 110 may be prevented from sagging by increasing the thickness of the board to make it stiffer or by affixing a vinyl chloride sheet or like reinforcement to the entire surface of the board. Nevertheless, this increases the weight of the wiring board 110 itself to give a greater burden to the movable frame or impede stable movement of the frame and other movable optical members such as the mirrors 104 and 105.
These problems are encountered not only with the analog copying machine described above but also with other apparatus wherein the flexible printed wiring board is attached as bent or folded over to a movable member. For example, similar problems are experienced with the flexible printed wiring boards used for the optical systems of digital copying machines or facsimile systems, or the printing heads of serial printers.